Unified Theory and Model for Anaerobic Hydrolysis in Municipal Wastewater Treatment: Review of Enzymological Aspects and Hydrolysis Assessments

Exploring the impact of bulk and substrate physics on hydrolysis rates and biogas yields of anaerobic digesters pretreated with thermal hydrolysis

“…As shown in Figure 6b, the condition with large solid BSA particles as the feed took approximately 14 hr longer to reach its maximum biogas production rate compared to the condition with small solid BSA particles as the feed. This difference demonstrated that there was a hydrolysis limitation acting in the first part of the biogas production rate curve, associated with colonization of the substrate, as described by Teo (2016). These results indicated that the colonization of the substrate on the macro-scale continued to affect the hydrolysis performance, regardless of the substrate's molecular structure.…”

“…As presented by Mancell‐Egala et al (), altering the bulk physical characteristics within the digester by increasing the biomass concentration increases the chances for collisions. According to Teo ()’s hydrolysis model, increased collisions between microbes and substrate would allow faster colonization, faster hydrolysis, and increased biogas production rates. However, as shown in the data presented in Table , there were no statistically significant differences observed in biogas yields, end rates, nor time of end rates, for AD sludge with TS concentrations ranging between 5% and 10% when mixed at 73/s.…”

“…Based on the hydrolysis model described by Teo (), it was proposed that modifying the bulk physical characteristics of the sludge within the digester through increasing the average floc size of the digestate would result in the contents of multiple smaller flocs being encompassed into one large floc, increasing the concentration of substrates and microbes within it, and decreasing the ability for external forces to disrupt the hydrolysis process (Mancell‐Egala et al, ). These increased concentrations within the flocs would allow faster colonization due to the decreased distance and decreased drag forces.…”

“…Disintegration and solubilization may occur simultaneously or in series. For solubilization to take place, two processes must happen in series: (a) Microbes must reach the surface of the particulate organic matter in a process referred to as colonization, and (b) once attached to the substrate, the microbes must secrete enzymes to oxidize the matter and convert it into soluble matter in a process referred to as enzyme secretion (Teo, ). The colonization rate is the time required for microbes within a digester to begin solubilizing the most available substrate, resulting in the maximum biogas production rate.…”

“…The product of each microbial step in AD serves as the substrate for the microbes in the next step. During the first step in the AD process, hydrolysis, particulate organic matter is converted into smaller particulates and ultimately into solubilized organic matter (Teo, ). The portion of the hydrolysis process wherein large particulates are converted into smaller particulates is referred to as disintegration, while the portion of the hydrolysis process wherein particulates are converted into soluble organic matter is referred to as solubilization.…”